1. Field of the Invention
The present invention relates to a multi charged particle beam writing method and a multi charged particle beam writing apparatus. More specifically, for example, the present invention relates to a blanking method in writing with multiple beams.
2. Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in the semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. The electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” a pattern on a wafer and the like with electron beams.
As an example employing the electron beam writing technique, a writing apparatus using multiple beams (multi-beams) can be cited. Compared with the case of writing a pattern by using a single electron beam, since it is possible to emit multiple beams at a time in multiple writing, the throughput can be greatly increased. In the writing apparatus employing a multi-beam system, for example, multiple beams are formed by letting an electron beam emitted from an electron gun assembly pass through a mask with a plurality of holes, blanking control is performed for each of the beams, and each unblocked beam is reduced by an optical system and deflected by a deflector so as to irradiate a desired position on a target object or “sample” (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2006-261342).
In the multi-beam writing, the dose of an individual beam is individually controlled by an irradiation time. For highly accurately controlling the dose of each beam, it is necessary to carry out blanking control at high speed to perform a beam ON/OFF control. Conventionally, in a writing apparatus of a multi-beam system, a blanking control circuit for each beam is placed on a blanking plate where each blanking electrode of multiple beams is arranged. Controlling is asynchronously performed for each beam. For example, a trigger signal for causing a beam to be ON is sent to control circuits of all the beams. In responsive to the trigger signal, the control circuit of each beam applies a beam-on voltage to an electrode and, simultaneously, starts counting the irradiation time period by a counter. Then, when the irradiation time has been completed, a beam-off voltage is applied. In performing such a control, a 10-bit control signal has been used, for example. However, since the space for placing a circuit on a blanking plate and the amount of current to be used are restricted, there is no other alternative but to have an uncomplicated circuit for the amount of information of control signals. Therefore, it has been difficult to build in a blanking circuit that can perform an operation of high speed and high precision. Further, installing a blanking control circuit for each beam on a blanking plate restricts to narrow the pitch of multiple beams. By contrast, when placing a control circuit for each beam outside the writing apparatus body and connecting each of them by wiring in order to secure a space for installing the circuit, since the wiring becomes long, there is a problem that a crosstalk problem becomes more prominent.